1. Field of the Invention
The present invention relates to energy storage systems, and more particularly to an energy storage system which stores electrical as mechanical energy and converts the mechanical energy to electrical energy as required.
2. Description of the Prior Art
To avoid motion artifacts (blurring due to motion of the patient) x-ray exposures should be as short as possible. The x-ray flux required to properly expose a film is fixed. Therefore, the intensity during short exposures must be very high. To obtain these high intensities the x-ray unit must have adequate electrical power during the exposure. A stationary x-ray unit with maximum ratings of 125 Kilovolts (peak) and 300 milliamps at 100 Kilovolts (peak) is considered a low-powered unit. Even these low-power units require an electrical supply with a capacity of over 20 Kilowatts. In most practical applications a 30 Kilowatt capacity would actually be provided for the unit.
The output ratings of even the most powerful mobile x-ray units are generally much less than those of relatively low-power stationary units. This is due primarily to the great expense involved in providing a large number of high capacity electrical outlets throughout a hospital. Other power sources are used in existing mobile units, but each of them has certain disadvantages that limit the practical output levels that can be achieved.
Most, if not all, existing mobile x-ray units fall into one of the three following general types:
(1) Wall outlet powered;
(2) Battery powered; and
(3) Capacitor discharge.
The wall outlet powered units are very similar to conventional stationary units. They consist of an integrated generator, tubestand and tube all mounted on a wheeled base. A power cord from the generator is plugged into a wall outlet to obtain electric power for the unit. These units have good outputs for their size and weight, but they are limited by the capacity of the outlet, high capacity outlets being very expensive. Usually only a few high capacity outlets are available in most hospitals, usually restricted to areas such as operating and emergency rooms.
Battery powered machines use a power cord only while the batteries are being recharged, usually at night, and require only a one Kilowatt outlet. They also provide emergency x-ray capability during power failures. However, several hundred pounds of batteries are required to obtain moderate x-ray outputs, the weight requirement being imposed by the basic properties of batteries. Also the batteries cannot be rapidly charged without damaging them, and their rate of discharge is limited by internal resistance.
Capacitor discharge units are severely limited by the amount of energy that can be stored in a capacitor of reasonable size and weight. The capacitor is initially charged to some value of high voltage, and then discharged through the x-ray tube. This produces a decrease in tube potential during the exposure. To obtain even very low exposures the voltage must be dropped by an appreciable amount, severely limiting the applications of these units.